Understanding Cathodic Protection
Cathodic protection is an electrochemical technique that prevents corrosion by converting the pipeline surface into a cathode of an electrical circuit. Corrosion occurs when metal loses electrons due to reactions with its environment. By supplying electrons from an external source, cathodic protection stops this process and significantly extends pipeline life.
There are two main types of cathodic protection systems:
- Galvanic (Sacrificial Anode) Systems
- Impressed Current Cathodic Protection (ICCP) Systems
The selection depends on pipeline size, soil resistivity, coating condition, and service life requirements.
Step 1: Pipeline Surface Preparation and Coating
Before installing Cathodic protection the pipeline must be properly coated. High-quality pipeline coatings reduce current demand and improve overall corrosion protection efficiency. Common coatings include fusion-bonded epoxy (FBE), polyethylene, and coal tar enamel.
Any coating defects should be identified and repaired, as bare metal areas are more susceptible to corrosion.
Step 2: System Design and Site Survey
A detailed site survey is conducted to evaluate soil resistivity, pipeline length, operating conditions, and environmental factors. Based on this data, engineers design a cathodic protection system that delivers adequate protective current across the entire pipeline.
Proper system design ensures uniform corrosion protection and prevents under-protection or over-protection.
Step 3: Installing Anodes
For galvanic systems, sacrificial anodes made of magnesium, zinc, or aluminum are buried near the pipeline. These anodes corrode instead of the pipeline, providing continuous cathodic protection.
In impressed current systems, durable anodes are installed in ground beds, and a DC power source (rectifier) supplies current to the pipeline. This method is commonly used for long pipelines requiring higher current output.
Step 4: Electrical Connections and Bonding
Electrical cables are connected between the pipeline and the anodes. All connections must be mechanically secure, electrically conductive, and properly insulated to avoid current loss. Test leads are also installed at designated test stations to allow monitoring of corrosion protection levels.
Proper bonding between pipeline sections ensures continuous electrical continuity throughout the system.
Step 5: System Commissioning and Testing
After installation, the cathodic protection system is energized and tested. Pipe-to-soil potential measurements are taken to confirm that the pipeline meets industry protection criteria. Adjustments are made to optimize current output and ensure effective corrosion protection.
Regular testing during commissioning helps identify installation issues early.
Step 6: Monitoring and Maintenance
Cathodic protection is not a one-time solution. Periodic inspections, potential surveys, and system adjustments are required to maintain effective corrosion protection over the pipeline’s service life. Anodes may need replacement, and rectifier outputs must be monitored to ensure continuous protection.
Conclusion
Installing cathodic protection on pipelines is a proven and essential method of corrosion protection. When properly designed, installed, and maintained, cathodic protection significantly reduces corrosion risks, enhances pipeline safety, and lowers long-term maintenance costs. Investing in a well-engineered cathodic protection system ensures reliable pipeline operation and regulatory compliance for years to come.